The present invention relates to a thin film transistor of active matrix liquid crystal display and, more particularly to a thin film transistor used in active matrix liquid crystal display, which comprises a two laminated structure of insulating layer coated on gate electrode, and amorphous silicon (hereinafter referred to as "a-Si") layers doped with phosphorus or boron at a predetermined rate and SiN layer of desirable thickness formed between said amorphous silicon layers having upper and lower layers.
Generally, an active matrix liquid crystal display (hereinafter referred to as "active matrix LCD") having a thin film transistor has been used for a display device of a television set, since it may be embodied due to its low consumption driving, thin film, light weight and high quality imaging properties.
However, when such a thin film of active matrix LCD is manufactured, there is a general problem that the production yield is low due to the need to carry out several photography etching processes.
The laminated structure of a gate insulating layer of a thin film transistor (hereinafter referred to as "TFT"), which is manufactured by the above mentioned process, not only extremely effects its characteristics, but electrically isolates the cross points between the gate electrode and the source electrode.
However, a problem with the said TFT is the short circuiting in the cross point between the gate electrode and the source electrode due to the weakening of the gate electrode and a-Si layer.
In addition, the conventional TFT is fabricated with only one SiO.sub.2 layer as the gate insulating layer. Therefore, when a threshold voltage in accordance with the operation of the TFT is in excess of 5 volts, the electron mobility is less than the range of 0.1 to 0.3 cm.sup.2 /v.sec.
The TFT under said operating condition may be able to drive a liquid crystal panel, but an LCD embodying the said TFT may not be able to enhance the manufacturing yield and high quality of the LCD.